Optical recording/reproducing method for multiple recording media with different recording density

ABSTRACT

An optical recording and reproducing method is able to record and reproduce information by using an optical system using recording and reproducing light with a wavelength selected in a range of from 780 nm±10 nm and an objective lens with a numerical aperture NA selected in a range of from 0.45±0.01 and records and reproduces first and second optical recording mediums having different recording capacities. The first optical recording medium is constructed by using a substrate with a track pitch Tp 1  being selected in a range of from 1.5 μm to 1.7 μm and a groove depth d 1  being selected in a range of from 70 nm to 90 nm, and the second optical recording medium is constructed by using a substrate  11  with a track pitch Tp 2  being selected in a range of from 1.2 μm to 1.3 μm and a groove depth d 2  of the groove  12  being selected in a range of from 150 nm to 180 nm. This, the optical recording medium has compatibility with existing optical discs and has a recording density high enough to record a moving picture.

The subject matter of application Ser. No. 10/503,265 is incorporatedherein by reference. The present application is a continuation of 371U.S. National Stage Application Ser. No. 10/503,265, filed Aug. 2, 2004,now U.S. Pat No. 7,113,470 claiming priority to PCT/JP03/01246 filedFeb. 6, 2003, which claims priority to Japanese Patent Application No.2002-030032, filed Feb. 6, 2002. The present application claims priorityto these previously filed applications.

TECHNICAL FIELD

The present invention relates to an optical recording and reproducingmethod that can be applied to a magneto-optical disc, widely used atpresent, such as an MD (Mini Disc), and particularly to an opticalrecording and reproducing method and an optical recording medium inwhich an optical system for use in recording and reproducing informationhas a wavelength selected in a range of from 780 nm±10 nm and anobjective lens with a numerical aperture NA selected in a range of from0.45±0.01.

BACKGROUND ART

As mediums for recording information such as music information,magneto-optical discs are widely used in the form of MDs, for exampleand are becoming very popular in Japan and foreign countries. Hence, theamount of information recorded on these magneto-optical discs isbecoming very large. From a technological standpoint, on the backgroundof the times in which the magneto-optical discs such as the MD have beenput on the market at the beginning, an optical system for use with anapparatus for recording and reproducing a magneto-optical disc uses anLD (Laser Diode) having a wavelength of 780 nm as a light source andalso uses an objective lens having a numerical aperture NA of 0.45.

Also, in the magneto-optical recording format such as the ISO, therehave been proposed a method in which an information recording mark isrecorded on a guide groove formed on the substrate of a magneto-opticalrecording medium, i.e. so-called groove and a method in which aninformation recording mark is recorded on a land formed between thegrooves. In addition, Official Gazette of Japanese laid-open patentapplication No. 10-320780, etc. have proposed a method in which aninformation recording mark is recorded on both of a land and a groove.In the MD, information is recorded on the groove, and a distance betweenthe grooves, that is, a track pitch Tp is selected to be approximately1.6 μm.

It has been requested that such MD should be modified into the systemcapable of recording a moving picture and the like from an accessibilitystandpoint. The most important point of the points at which the systemshould be modified is to increase a recording density of amagneto-optical disc. While music information needs a recording densityof approximately 100 MB, a moving picture requires a recording densityof at least about 10 times as high as the above-mentioned recordingdensity depending upon image quality. Although various methods have beenso far proposed in order to achieve these requirements, one of suchpreviously-proposed methods is a magnetically induced super resolutionreproducing system, that is, a so-called MSR (Magnetically induced SuperResolution) system that is proposed in Japanese Patent No. 2805746, forexample.

The MSR system will be described below in brief. According to thistechnology, a recording and reproducing film of a magneto-optical diskis comprised of a plurality of magnetic layers having proper coerciveforce, proper exchange-coupling force, a Curie temperature and the like,for example, a recording layer and a reproducing layer or anintermediate layer interposed between the recording layer and thereproducing layer. This technology uses the fact that a temperatureproduced on the recording and reproducing film on the magneto-opticaldisc with irradiation of reproducing laser light changes depending onthe positions within the irradiated spot. Magnetization of the recordinglayer is transferred to the reproducing layer only in a certain limitedtemperature region. In the temperature region outside this temperatureregion, regardless of magnetizations of the recording layer, themagnetizations of the reproducing layer are arrayed in one direction,for example, to produce a magnetic mask on a part of the inside of aso-called irradiated spot. Thus, even when a plurality of marks isformed within the spot, it becomes possible to reproduce a part of therecording marks, thereby improving a resolution.

With respect to the above-mentioned MSR system, various systems havebeen proposed, which will be described below.

Official Gazette of Japanese laid-open patent application No. 1-143042has proposed a so-called FAD (Front Aperture Detection) system whichdetects recording marks located ahead of the direction in which theirradiated spot is moved. According to the FAD system, a magneto-opticalrecording layer is composed of magnetic layers of a tri-layer structurecomprising a reproducing layer made of GdFeCo or the like, anintermediate switching layer made of TeFeCoAl or the like and arecording layer made of TeFeCo or the like. When a laser spot isirradiated on a rotating disc-like medium, a high temperature region isslightly displaced rearwards from the center of the spot due to heatconductivity. In the high temperature region within this spot, since thetemperature of the intermediate switching layer rises in excess of theCurie temperature, the exchange-coupling force between the reproducinglayer and the recording layer decreases so that magnetizations of thereproducing layer selected to be the material with small coercive forceare arrayed by reproduced magnetic fields and thereby information iserased, that is, masked. As a result, only the magnetizations of therecording marks of the front portion which is the low temperature regioncan be detected in the state in which they were transferred to thereproducing layer, and hence super resolution becomes possible.

Also, Official Gazette of Japanese laid-open patent application No.5-81717, Official Gazette of Japanese laid-open patent application No.5-12731 and the like, for example, have proposed a so-called CAD (CenterAperture Detection) system in which magnetization of a reproducing layerchanges from surface magnetization to perpendicular magnetization onlyin the high temperature region at the central portion of the irradiationspot to read only recording marks from this portion.

Further, Official Gazette of Japanese laid-open patent application No.3-90358, Official Gazette of Japanese laid-open patent application No.4-271039 and the like, for example, have proposed a so-called RAD (RearAperture Detection) system for detecting rear recording marks of thespot.

On the other hand, Official Gazette of Japanese laid-open patentapplication No. 4-255946 and Official Gazette of Japanese laid-openpatent application No. 4-271039 and the like, for example, have proposeda so-called D-RAD (Double mask Rear Aperture Detection) system in whicha magneto-optical recording layer is composed of a recording layer, anintermediate layer and a reproducing layer. Upon reproduction, in thestate in which the reproducing layer is magnetized in one direction, areproducing magnetic field is applied to the reproducing layer along themagnetization direction to produce a low temperature region, areproducible region and a high temperature region in the regionirradiated with the illumination spot, a sum of the reproducing magneticfield and coercive force of the reproducing layer becomes small only inthe reproducible region as compared with a magnetic field produced by amagnetic wall between the reproducing layer and the intermediate layerformed just under the reproducing layer, whereby the magnetization ofthe recording layer in this reproducible region is transferred to thereproducing layer to thereby reproduce information by a magneticallyinduced super resolution system.

An optical recording medium using this D-RAD system has already beencommercially available on the market as an optical recording mediumcalled “GIGAMO” (trade name and produced by Sony Corporation).

Further, Official Gazette of Japanese laid-open patent application NO.6-290469 and the like, for example, have proposed a so-called DWDD(Domain Wall Displacement Detection) system in which a reproducing layeris made of a material of which domain wall coercive force is small andwhose domain wall displacement degree is large as compared with those ofa recording layer, a Curie temperature of an intermediate layer betweenthe reproducing layer and the recording layer is selected to be small ascompared with those of the reproducing layer and the recording layer andthe magnetic domain of the reproducing layer is enlarged in theintermediate layer within the irradiated spot at its high temperatureregion of which temperature rises in excess of the Curie temperature toread out the magnetization of the recording layer.

Furthermore, Official Gazette of Japanese laid-open patent applicationNo. 8-7350 and the like, for example, have proposed a so-called MAMMOS(Magnetic Amplifying MO System) system in which a magnetic domain of arecording layer is transferred to a reproducing layer by effectivelyutilizing an external magnetic field and in which the magnetic domaintransferred to this reproducing layer is enlarged to read out themagnetization of the recording layer.

On the other hand, there are requests of effectively utilizing andkeeping property such as information diffused on the whole world bymagneto-optical discs such as the conventional MD, and the appearance ofan apparatus or a method or a medium using this apparatus and methodthat can use moving pictures while the property of the above informationcan be used has been desired. That is, while keeping compatibility withthe existing MD, the above medium is requested to increase only arecording density approximately 10 times.

It has been customary for the MD recording and reproducing apparatus touse the optical system using a light source with a wavelength selectedto be 780 nm and an objective lens with a numerical aperture NA selectedto be 0.45 as described above. Similarly to other optical discs, a shapeof a focused beam spot is substantially determined by a wavelength of alight source and a numerical aperture of an objective lens.

After the shape of the beam spot is determined, the track pitch that canbe used in that spot and the shortest pit length corresponding to alinear density are determined. In the case of the MD, the track pitch issubstantially 1.6 μm, and the shortest bit length is 0.59 μm. Theshortest bit length is determined by an MTF (Modulation TransferFunction: modulation transfer function) at the determined spot and themodulation-and-demodulation. With this bit length, when this opticalsystem is used, it is possible to obtain a sufficient reproduced signal.

Also, a track pitch is selected in a range in which tracking can beachieved by the determined spot. Tracking uses a difference betweenreflectivities between the land and the groove, and not only the trackpitch conditions but also the groove depth condition are added. A reportentitled “The Main Point of Setting of Optical Pickup System” (compiledunder the supervision of Mr. Noda, Electronics Essential Series No. 6,Japan Industry Engineering Center, 1984) has described the study thatwhen a wavelength of light is λ and a refractive index of a substrate isn, then a signal is lost if the groove depth is set to be λ/4 n.

Although the track pitch Tp and the shortest bit length are determinedas described above, both of them should be decreased because of thedemand of increasing a recording density. It is possible to decrease thetrack pitch to about 1.2 μm in a range in which a reproducing signalused to apply tracking can be held stably.

However, if the track pitch is reduced to 1.2 μm, then phenomenon inwhich upon reproduction, the adjacent track is affected by heat andinformation is recorded on the adjacent track, that is, so-calledcross-write will occur unavoidably.

Although the cross-write is not a serious problem when a recording markis not formed on the adjacent track, if information is recorded on theadjacent track, then such recorded information is broken, and hence thecross-write is a problem that should be prevented from a reliabilitystandpoint.

It is an object of the present invention to provide an optical recordingand reproducing method and an optical recording medium for use with theabove optical recording and reproducing method in which theabove-mentioned problems can be solved, which have compatibility withexisting and most widely-used magneto-optical disc such as an MD, inwhich high density recording is possible, that is, a recording capacityis increased to make recording and reproduction of a moving picturebecome possible. Further, it is another object of the present inventionto provide an optical recording and reproducing method and an opticalrecording medium for use with the above optical recording andreproducing method in which the occurrence of cross-write can be avoidedand which is excellent in recording and reproducing characteristic.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided an opticalrecording and reproducing method for recording and reproducinginformation by an optical system using recording and reproducing lightwith a wavelength selected in a range of from 780 nm±10 nm and anobjective lens with a numerical aperture NA selected in a range of from0.45±0.01 and in which first and second optical recording mediums havingdifferent recording capacities are recorded and reproduced. The firstoptical recording medium is constructed by using a substrate with atrack pitch selected in a range of from 1.5 μm to 1.7 μm and a groovedepth selected in a range of from 70 nm to 90 nm, and the second opticalrecording medium is constructed by using a substrate with a track pitchselected in a range of from 1.2 μm to 1.3 μm and a groove depth selectedin a range of from 150 nm to 180 nm.

Also, according to the present invention, in the above-mentioned opticalrecording and reproducing method, the shortest recording bit length ofthe second optical recording medium is selected to be less than a bitlength corresponding to a cut-off frequency of a modulation transmissionfunction of the optical system.

Further, according to the present invention, in the above-mentionedrespective optical recording and reproducing methods, the first andsecond optical recording mediums are constructed as magneto-opticalrecording mediums.

Also, according to the present invention, in the above-mentionedrespective optical recording and reproducing methods, the first opticalrecording medium has at least a first dielectric layer, amagneto-optical recording layer, a second dielectric layer and a thermaldiffusion layer deposited on a substrate, in that order. The secondoptical recording medium has at least a first dielectric layer, a firstmagneto-optical recording layer, a second magneto-optical recordinglayer, a third magneto-optical recording layer and a second dielectriclayer deposited on a substrate, in that order. A Curie temperature ofthe second magneto-optical recording layer is selected to be small ascompared with those of the first and third magneto-optical recordinglayers.

Further, according to the present invention, in the above-mentionedrespective optical recording and reproducing methods, themagneto-optical recording layer of the first optical recording medium ismade of TbFeCo or TbFeCoCr, the first magneto-optical recording layer ofthe second optical recording medium is made of any one of GdFeCo, GdFe,GdFeCoCr, GdFeCoAl or GdFeCoSi, the second magneto-optical recordinglayer of the second optical recording medium is made of any one of TbFe,TbFeCo, TbFeAl, TbFeCr, TbFeSi, TbFeCoAl, TbFeCoCr or TbFeCoSi. Thethird magneto-optical recording layer of the second optical recordingmedium is made of either TbFeCo or TbFeCoCr.

Also, according to the present invention, in the above-mentionedrespective optical recording and reproducing methods, the second opticalrecording medium is constructed as the magneto-optical recording mediumin which information is reproduced by a magnetically induced superresolution system and which has a recording capacity greater than 1 GB.

Further, according to the present invention, in the above-mentionedrespective optical recording and reproducing methods, the second opticalrecording medium is constructed as the magneto-optical recording mediumin which information is recorded by a groove recording system.

Furthermore, according to the present invention, in the above-mentionedrespective optical recording and reproducing methods, the second opticalrecording medium is constructed as the magneto-optical recording mediumin which information is recorded by a land-groove recording system.

Also, the optical recording medium according to the present invention isan optical recording medium that is recorded and reproduced by anoptical system using recording and reproducing light with a wavelengthselected in a range of from 780 nm±10 nm and an objective lens with anumerical aperture NA selected in a range of from 0.45±0.01 and theoptical recording medium is constructed by using a substrate with atrack pitch selected in a range of from 1.2 μm to 1.3 μm and a groovedepth selected in a range of from 150 nm to 180 nm.

Further, according to the present invention, in the above-mentionedoptical recording medium, the shortest recording bit length of recordinginformation is selected to be less than a bit length corresponding to acut-off frequency of a modulation transmission function of theabove-described optical system.

Also, according to the present invention, the above-mentioned opticalrecording medium is constructed as a magneto-optical recording medium.

Furthermore, according to the present invention, the above-mentionedoptical recording medium has at least a first dielectric layer, a firstmagneto-optical recording layer, a second magneto-optical recordinglayer, a third magneto-optical recording layer and a second dielectriclayer deposited on a substrate, in that order, and a Curie temperatureof the second magneto-optical recording layer is selected to be small ascompared with those of the first and third magneto-optical recordinglayers.

Also, according to the present invention, the first magneto-opticalrecording layer of the above-mentioned optical recording medium is madeof any one of GdFeCo, GdFe, GdFeCoCr, GdFeCoAl or GdFeCoSi, the secondmagneto-optical recording layer is made of any one of TbFe, TbFeCo,TbFeAl, TbFeCr, TbFeSi, TbFeCoAl, TbFeCoCr or TbFeCoSi and the thirdmagneto-optical recording layer is made of either TbFeCo or TbFeCoCr.

Further, according to the present invention, the above-mentioned opticalrecording medium is constructed as a magneto-optical recording medium inwhich information is reproduced by a magnetically induced superresolution system and which has a recording capacity greater than 1 GB.

Also, according to the present invention, the above-mentioned opticalrecording medium is constructed as a magneto-optical recording medium inwhich information is recorded by a groove recording system.

Furthermore, according to the present invention, the above-mentionedoptical recording medium is constructed as a magneto-optical recordingmedium in which information is recorded by a land-groove recordingsystem.

As described above, according to the present invention, information isrecorded and reproduced by the optical system using the recording andreproducing light with the wavelength selected in a range of from 780nm±10 nm and the objective lens with the numerical aperture NA selectedin a range of from 0.45±0.01 similarly to the optical system in theconventional MD recording and reproducing system, the existing opticalrecording medium, which is widely used, such as the so-called MD inwhich the first optical recording medium is constructed by using thesubstrate with the track pitch selected in a range of from 1.5 μm to 1.7μm and the groove depth selected in a range of from 70 nm to 90 nm canbe recorded and reproduced, that is, the present invention hascompatibility with other suitable recording and reproducing mediums suchas the MD. At the same time, the optical recording medium constructed byusing the second optical recording medium having a recording capacitydifferent from that of the first recording medium, that is, thesubstrate with the track pitch selected in a range of from 1.2 μm to 1.3μm and the groove depth selected in a range of from 150 nm to 180 nmalso can be recorded and reproduced, and hence it becomes possible torecord and reproduce next-generation optical recording mediums, whichcan be increased in recording density, by the recording and reproducingapparatus having the same optical system.

Further, since the groove depth of the optical recording medium in whichthe track pitch was reduced to approximately 1.2 μm to 1.3 μm in orderto increase a recording density is selected in a range of from 150 nm to180 nm as described above, the occurrence of the cross-write can besuppressed while the reproducing signal for applying tracking when theoptical recording medium is recorded and reproduced can be held stably,and hence a recording and reproducing characteristic could be heldsatisfactorily.

Accordingly, by using the optical recording medium that can stably berecorded and reproduced by the compatible recording and reproducingapparatus, it becomes possible to use conventional information widelyand at the same time, moving picture information and the like, whichrequires a large capacity, can be recorded and reproduced. Hence, it ispossible to provide the optical recording and reproducing method and theoptical recording medium which are extremely useful in actual practice.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing an arrangement of an example of anoptical recording medium;

FIG. 2 is a schematic diagram showing an arrangement of an example of anoptical recording medium;

FIG. 3 is a diagram showing carrier and crosstalk characteristicsrelative to a groove depth of an example of an optical recording medium;

FIG. 4 is a diagram showing a recording characteristic of an example ofan optical recording medium;

FIG. 5 is a diagram showing a recording characteristic of an example ofan optical recording medium;

FIG. 6 is a diagram showing recording a recording characteristic of anexample of an optical recording medium;

FIG. 7 is a diagram showing a recording characteristic of an example ofan optical recording medium;

FIG. 8 is a diagram showing a recording characteristic of an example ofan optical recording medium;

FIG. 9 is a diagram showing a reproducing characteristic of an exampleof an optical recording medium;

FIG. 10 is a diagram showing a reproducing characteristic of an exampleof an optical recording medium;

FIG. 11 is a diagram showing a reproducing characteristic of an exampleof an optical recording medium; and

FIG. 12 is a diagram showing a reproducing characteristic of an exampleof an optical recording medium.

BEST MODE FOR CARRYING OUT THE INVENTION

An optical recording and reproducing method and an optical recordingmedium for use with this optical recording and reproducing method willbe described below with reference to the drawings. While the MD isapplied to the first optical recording medium and the MSR system FAD andD-RAD system magneto-optical recording medium are applied to the secondoptical recording medium in the following examples, the presentinvention is not limited to these respective examples. For example, anoptical recording medium using a pigment material layer as a recordinglayer may be used as the first optical recording medium or an opticalrecording medium based on the MSR system such as the CAD system and theRAD system may be used as the second optical recording medium.

FIGS. 1 and 2 are schematic diagrams showing an arrangement of anexample of a first optical recording medium for use with an opticalrecording and reproducing method of the present invention. In FIG. 1,reference numeral 1 denotes a substrate on which a first dielectriclayer 3, a magneto-optical recording layer 4, a second dielectric layer5 and a thermal diffusion layer 6 are deposited, in that order, by aphysical film deposition method such as a sputtering method. On thethermal diffusion layer, there is deposited a protective film 7 by asuitable method such as a spin-coating method and thereby a firstoptical recording medium 10 is constructed.

Also, as shown in FIG. 2, on a substrate 11, there are deposited a firstdielectric layer 13, a reproducing layer 14, that is, a firstmagneto-optical recording layer, an intermediate switching layer 15,that is, a second magneto-optical recording layer, a recording layer 16,that is, a third magneto-optical recording layer, a second dielectriclayer 17 and a thermal diffusion layer 18 by a physical film depositionmethod such as a sputtering method, in that order. On the thermaldiffusion layer, there is deposited a protective layer 19 by a suitablemethod such as a spin-coating method and thereby a second opticalrecording medium 20 is constructed.

The substrates 1 and 11 are molded as disc-like substrates made of aresin material such as ZEONEX and polycarbonate by a suitable methodsuch as an injection molding method. Refractive indexes of thesesubstrates can be selected in a range of from 1.45 to 1.65, thicknessesthereof can be selected in a range of from 1.1 to 1.3 mm andbirefringence thereof can be selected to be approximately 100 nm.

It is customary that the first dielectric layers 3 and 13 of therespective mediums 10 and 20 are made of SiN, SiO₂ and refractiveindexes thereof are approximately 2.0.

The magneto-optical recording layer 4 of the first optical recordingmedium is made of TbFeCo, TbFeCoCr and the like, for example, and has afilm thickness of about 20 nm, for example.

The reproducing layer 14 of the second optical recording medium 20 ismade of a material having a large Kerr rotation angle, such as Gd₂₂(FeCo₂₀) with superiority of a transition metal in order to enhance areproducing signal, a Curie temperature thereof is set to be greaterthan 300° C., for example, 320° C. and a film thickness thereof isselected to be approximately 30 nm, for example. GdFeCo may contain anadditive such Cr, as Al, Si, and this reproducing layer can also be madeof GdFe.

The intermediate switching layer 15 of the second optical recordingmedium 20 may be made of Tb₂₀(FeCo₂)₇₇Al₁₃, a Curie temperature Tcthereof is selected to be lower than any one of Curie temperatures ofthe reproducing layer 14 and the recording layer 16, for example, 140°C. Al, Si, Cr and the like may be added as the additives and TbFe,TbFeAl, TbFeCr, TbFeSi may be used sometimes. A film thickness of thisintermediate switching layer is selected to be 10 nm, for example.

The recording layer 16 of the second optical recording medium 20 may bemade of Tb₂₀ (FeCo₂₅) such as Tb₂₀ (FeCo₂₅), Tb₂₀(FeCo₂₅)_(78.5)Cr_(1.5) and a film thickness thereof is selected to be20 nm, for example. A Curie temperature of this recording layer is 270°C. and a coercive force thereof at room temperature is 1.6 MA/m.

The second dielectric layers 5 and 17 of the first and second opticalrecording mediums 10 and 20 are made of a suitable material such as SiNor SiO₂ similarly to the first dielectric layer. These layers areprovided not only in order to enhance a reproducing signal but also inorder to prevent moisture from reaching the recording layer.

Further, the thermal diffusion layers 6 and 18 of the two mediums areformed by depositions of metals such as Al and AlTi. These layers areprovided not only in order to make optical multiplex reflection but alsoin order to make thermal adjustment to enable recording marks of adesired size to be formed stably.

The protective layers 7 and 19 are made of an ultraviolet-curing resin,for example, and have film thicknesses ranging from approximately 10 to20 μm. The protective layers 7 and 19 are provided not only in order toprevent moisture from entering the mediums but also in order to enable amagnetic head to move slidably with ease and also to prevent therecording layer from being damaged by mechanical scratches produced bythe slidable movement of the magnetic head. If the protective layers aretoo thin, then they will become fragile. If they are too thick, thenthey will become heavy, and hence their film thicknesses are controlledso as to fall within a proper range of film thickness.

Then, grooves 2 are formed on the substrate 1 of the first opticalrecording medium 10 concentrically or spirally. A track pitch Tp₁ of thegrooves 2 is selected in a range of from 1.5 μm to 1.7 μm for example,approximately 1.6 μm, and a depth d₁ thereof is selected in a range offrom 70 to 90 nm, for example, approximately 70 nm. An address signalfor use in storing information is recorded on the optical recordingmedium by wobbling by which the grooves are wobbled. In FIG. 1,reference numeral 8 denotes a land.

Grooves 12 are formed on the substrate 11 of the second opticalrecording medium 20 in such a manner that a track pitch Tp₂ thereof isselected in a range of from 1.2 to 1.3 μm, for example, approximately1.3 μm and that a depth d₂ thereof is selected in a range of from 150 to180 nm, for example, 170 nm. Reference numeral 21 denotes a land.

The reason that the track pitch Tp₂ of the second optical recordingmedium 20 is selected in a range of from 1.2 to 1.3 μm is to increase arecording density. Also, the above reason lies in the fact that, if thistrack pitch is less than 1.2 μm, then tracking cannot be achieved in anoptical system in which a wavelength λ is 780 nm, a numerical apertureNA being 0.45. Further, the above reason lies in the fact that, if theabove track pitch exceeds 1.3 μm, then it becomes difficult to increasea recording density.

The second optical recording medium 20 was recorded and reproduced in anFAD system by using an optical system with a light source having awavelength of 780 nm and an objective lens having a numerical apertureNA of 0.45 and a change of a reproducing characteristic relative to thegroove depth was measured.

More specifically, according to the above-mentioned arrangement, in thefirst magneto-optical recording layer of the second optical recordingmedium 20, that is, the reproducing layer 14, since the temperature ofthe intermediate switching layer 15 is raised in excess of the Curietemperature in the high temperature region within the spot irradiatedwith recording and reproducing light from the light source,exchange-coupling force between the reproducing layer 14 and therecording layer 15 is substantially reduced to zero and magnetizationsof the reproducing layer 14 selected by the material with the smallcoercive force are arrayed by the reproducing magnetic field and therebyinformation is erased, that is, masked. As a result, the change of thereproducing characteristic can be detected in the state in which onlythe magnetizations of the recording marks of the front portion which isthe low temperature region are transferred to the reproducing layer.

In this example, the reproducing layer 14 of the second opticalrecording medium 20 is the transition metal superiority film, thecoercive force thereof is held at 8 kA/m at room temperature, and theCurie temperature thereof is set to be 320° C. as described above. Theintermediate switching layer 15 is the transition metal superiority filmand the Curie temperature thereof is set to be 140° C. as describedabove.

In this example, the second optical recording medium 20 was constructedin such a manner that the shortest recording bit length of recordinginformation was selected to be 0.24 μm which is less than the bit lengthcorresponding to the cut-off frequency of the modulation transmissionfunction of the optical system, the recording capacity thereof was beingselected to be 670 MB.

FIG. 3 shows changes of carriers of a recorded and reproduced groove(main track) relative to the depth of the groove on the substrate 11 ofthe second optical recording medium 20 and relative outputs of a leakagesignal from the adjacent track (land), that is, crosstalk. In FIG. 3, asolid line a shows a carrier, and a solid line b shows a crosstalk.

A crosstalk appears not in the recording mode but only in thereproducing mode and cannot be canceled out completely regardless of thedepth of the groove unlike the aforementioned cross-write. However, astudy of the results on FIG. 3 reveals that a crosstalk signal has acertain tendency relative to the groove depth. More specifically, it isto be understood that, in the case of a certain groove depth, that is,about 100 nm and about 140 nm, the minimal value of the crosstalkappears. In the region in which the crosstalk is small, reproductionbecomes easy, and a reproducing characteristic can be improved.

On the other hand, a signal from the main track becomes small in thegroove depth of a certain range. From the results shown in FIG. 3, it isto be understood that the output becomes the minimum value when thegroove depth lies in a range of from approximately 120 to 130 nm.

It is to be expected that a reproduced signal can be obtained in theregion in which these characteristics are added together. If the carrierfrom the main track is large, then a reproduced signal can be used eventhough the crosstalk is large a little. Therefore, its evaluation indexcannot be obtained from the simple comparison of the relative outputs,and from the results of the experiments done by the inventors of thepresent application, it was to be understood that a small groove depthregion of 70 to 90 nm, more preferably, a small groove depth region ofabout 70 nm, a small groove depth region of 150 to 180 nm, morepreferably, a small groove depth region of 160 to 175 nm can be usedsatisfactorily.

Having considered the characteristics of the carrier and the crosstalk,it is to be expected that larger groove depth regions which can be usedin actual practice will exist intermittently. However, since groovesdeeper than the above groove depths are difficult to be produced by theexisting technologies such as the injection molding, it is desired thatthe groove depth should be less than 180 nm.

Also, while a region to record information may be either the land or thegroove of the substrate, if information is recorded on the groove, thenthis system for recording information on the groove has many pointscommon to the existing MD recording and reproducing system, which isthen advantageous for realizing compatibility.

Further, as the light source of the optical system for use with theabove-mentioned second optical recording medium, there can be usedlasers with different wavelengths such as 680 nm, 660 nm and 410 nminstead of the laser diode with the wavelength of 780 nm. Since thelaser with the wavelength of 780 nm has advantages in which its originallaser output is large, it has small power consumption and it isinexpensive, when the light source with the wavelength of 780 nm isused, there is a large merit to increase a high recording density of themedium for consumers.

Also, it can easily be expected that these large-storage capacityinformation recording mediums will frequently be used to record movingpictures. When the wavelength of the light source is selected to be 780nm, a margin for avoiding de-track and disc skew produced by vibrationsproduced when a moving picture is recorded increases more. Theinformation recording medium is advantageous for protecting it frombeing smudged by dusts or the like when the wavelength of the lightsource is similarly selected to be 780 nm.

In actual practice, the light source with the wavelength of 780 nmcannot avoid fluctuations of wavelength of ±10 nm due to dispersionsproduced in the manufacturing process at ordinary accuracy. Similarly,the numerical aperture of the objective lens also cannot avoidfluctuations of approximately ±0.01. For this reason, the presentinvention uses the optical system with the wavelength of 780 nm±10 nmand the numerical aperture NA of the objective lens of 0.45±0.01.

Next, the above-mentioned second optical recording medium 20 wasrecorded and reproduced by the above-mentioned FAD system and itsrecording and reproducing characteristic was examined.

FIGS. 4 and 5 show recording and reproducing characteristics obtainedwhen information is recorded on the grooves and the lands in the statein which the track pitch Tp₂ of the substrate 11 is selected to be 1.3μm and the groove depth d₂ thereof was selected to be 170 nm,respectively. In the recording and reproducing characteristic, shown inFIG. 4, obtained when information is recorded on the groove and therecording and reproducing characteristic, shown in FIG. 5, obtained wheninformation is recorded on the land, solid lines c and e show measuredresults of overwrite characteristics, that is, measured results ofjitter characteristics obtained when information is recorded on the maintrack while the power of the laser is being increased. Broken lines dand f show measured results of cross-write characteristics, that is,measured results of jitters on the main track after information has beenrecorded on the adjacent track by that power. More specifically, thosediagrams are graphs showing the measured results of the cross-writecharacteristics generated from the adjacent track to the main track.Measurement conditions are such that the linear velocity is 2.0 m/s, theshortest bit length being 0.16 μm as described above.

From the results shown in FIGS. 4 and 5, it is to be understood thatboth of the land and the groove have sufficient recording power margins.

On the other hand, we have examined recording and reproducingcharacteristics obtained when the groove depth was selected to be 70 nmsimilarly to the first optical recording medium 10 while the track pitchTp₂ was held small, that is, 1.3 μm. In FIGS. 6 and 7, solid lines g andI show measured results of overwrite characteristics and broken lines hand j show measured results of cross-write characteristics obtainedafter information has been recorded on the groove and the land,respectively. Measurement conditions were selected to be similar tothose of the above-mentioned examples of FIGS. 4 and 5.

From the results shown in FIGS. 6 and 7, it is clear that when thegroove depth d₂ of the second optical recording medium 20 is selected tobe the same as the groove depth d₁ of the first optical recording medium10, recording power to the main track and cross-write power from theadjacent track are very close to each other and the recording powermargin is small. There is then a large possibility that the system willbecome unable to function due to some external disturbance.Alternatively, there is a possibility that information will be erasedand hence there is a risk that the recording and reproducingcharacteristic cannot be held stably.

Accordingly, in the present invention, the groove depth d₂ of the secondoptical recording medium 20 of which recording capacity can be increasedrelatively is selected in a range of from 150 nm to 180 nm. Morepreferably, this groove depth should be selected in a range of from 160nm to 175 nm, whereby the recording and reproducing characteristic canbe made more stable.

Next, the material and arrangement of the second optical recordingmedium 20 which can be recorded and reproduced with super resolution bythe D-RAD system recording and reproducing system will be described inwhich case the above-mentioned arrangement shown in FIGS. 1 and 2 isused and the first optical recording medium 10 has the same material andarrangement as those of the above-mentioned example.

In this example, similarly to the above-mentioned example, the secondsubstrate is a disc-like substrate molded by an injection molding methodof a resin material such as ZEONEX and polycarbonate. A refractive indexof this second substrate is selected in a range of from 1.45 to 1.65, athickness thereof is selected in a range of from 1.1 to 1.3 mm, andbirefringence thereof is selected to be less than 30 nm.

In this example, a substrate 11 has a groove 12 with a track pitch Tp₂of 1.2 μm and a groove depth d₂ of 175 nm.

This substrate is set to a carrying sputtering system in which films areto be deposited on the substrate under high vacuum condition of higherthan 1×10⁻⁴ Pa.

First, a SiN film, for example, is deposited as a first dielectric layer13. This film is deposited from a Si target by a reactive sputteringmethod of a mixed gas of an Ar gas and an N₂ gas. A gas flow rate of theAr gas and the N₂ gas is selected to be 40:20. A film thickness of thisfilm is selected in a range in which a magneto-optical recordingcharacteristic of super resolution can be prevented from beingdeteriorated, for example, in a range of from 76 nm to 88 nm, forexample, 80 nm. Similarly to the above-mentioned example, this layerplays the role of not only optically enhancing the signal of themagneto-optical recording layer but also preventing moisture from thesubstrate from reaching the recording layer.

Next, a reproducing layer 14 is deposited as the first magneto-opticalrecording layer. A composition of this reproducing layer is Gd₂₄Fe₆₃Co₁₃and a film thickness thereof is selected to be 40 nm. A sputtering gasis an Ar gas. So long as the film thickness lies in a range of from 35nm to 48 nm, a magneto-optical recording characteristic can be preventedfrom being deteriorated. A film with a large Kerr rotation angle is usedas the reproducing layer 14.

A second magneto-optical recording layer is deposited. While theintermediate switching layer 15 is shown as the second magneto-opticalrecording layer in the example of FIG. 2, in this case, the intermediateswitching layer is made of a material which might be called anintermediate layer, for example, Gd₂₉Fe₆₀Co₂Si₉ and a film thicknessthereof is selected to be approximately 30 nm. A sputtering gas is an Argas. So long as the film thickness of this intermediate switching layeris selected in a range of from 29 nm to 36 nm, a magneto-opticalrecording characteristic can be prevented from being deteriorated.

Next, a recording layer 16 is deposited as a third magneto-opticalrecording layer. A composition of this recording layer is Tb₂₂Fe₆₃Co₁₅and a film thickness thereof is selected to be 46 nm, for example. Solong as the film thickness of this recording layer is selected in arange of from about 42 nm to 60 nm, a magneto-optical recordingcharacteristic can be prevented from being deteriorated.

Thereafter, a second dielectric layer 17 is deposited. A material andconditions for depositing this second dielectric layer can be selectedto be the same as those of the first dielectric layer 13, and a filmthickness thereof is selected to be 25 nm, for example.

Next, an AlTi film having a film thickness of 9 nm, for example, isdeposited as a thermal diffusion layer 18. In the last process, aprotective layer 19 made of an ultraviolet-curing resin, for example,having a film thickness ranging of from approximately 10 to 20 μm wasdeposited by a suitable method such as a spin-coating method and curedto construct the second optical recording medium 20.

The thus manufactured second optical recording medium 20 was recordedand reproduced by effectively utilizing super resolution reproductionbased on the above-mentioned D-RAD system and a recording andreproducing characteristic thereof was examined.

More specifically, when recorded information is reproduced, in the statein which the reproducing layer 14 is magnetized in one direction, areproducing magnetic field Hr is applied to the reproducing layer alongits magnetization direction to produce a low temperature region, areproducible region and a high temperature region in the regionirradiated with an illumination spot, a sum of the reproducing magneticfield Hr and coercive force H_(CA) of the reproducing layer 14 isdecreased only in the reproducible region as compared with a magneticfield H_(W1) of the magnetic wall between the reproducing layer and theintermediate layer adjoining the reproducing layer 1, that is, thesecond magneto-optical recording layer 15, the magnetization of therecording layer 16 is transferred to and detected in the reproducinglayer 14 only in the reproducible region within the reproducible regionand thereby super resolution reproduction is carried out.

In this example, the reproducing magnetic field Hr is 32 kA/m at roomtemperature, the coercive force H_(CA) of the reproducing layer 14 is 16kA/m at room temperature and the magnetic field H_(W1) produced by themagnetic wall between the reproducing layer 14 and the secondmagneto-optical recording layer 15 is 24 kA/m at room temperature.

Further, in this example, the shortest recording bit length of recordinginformation was selected to be 0.16 μm which is less than the bit lengthcorresponding to the cut-off frequency of the modulation transmissionfunction of the optical system, and the recording capacity is selectedto be 1.0 GB.

FIG. 8 shows byte error rates corresponding to recorded information onthe groove 12 and the land 21 when recording power is changed. A solidline k shows recorded information on the groove 12 and a broken line lshows recorded information on the land, respectively. A dash-and-dotline M shows a margin level. From FIG. 8, it is to be understood that asufficient recording power margin could be obtained.

Next, FIGS. 9 and 10 show measured results of reproducing power margins.FIG. 9 shows measured results obtained when recorded information wasreproduced from the groove. A solid line m shows measured resultsobtained when recorded information was reproduced from the groove with acrosstalk, and a broken line n shows measured results obtained whenrecorded information was reproduced from the groove without crosstalk.FIG. 10 shows measured results obtained when recorded information wasreproduced from the land. A solid line o shows measured results obtainedwhen recorded information was reproduced from the land with a crosstalk,and a broken line p shows measured results obtained when recordedinformation was reproduced from the land without crosstalk. In FIGS. 9and 10, a dash-and-dot line M shows a reproducing power margin level.From these measured results, it is to be understood that the magnitudeof the byte error rate is not so changed with or without crosstalk andthat a wide reproducing power margin can be obtained.

Next, FIGS. 11 and 12 show measured results of a de-track margin. FIG.11 shows measured results of a de-track margin obtained when recordedinformation was reproduced from the groove and the land. A solid line qshows measured results of the de-track margin obtained when recordedinformation was reproduced from the groove, and a broken line r showsmeasured results of the de-track margin when recorded information wasreproduced from the land. FIG. 12 shows measured results of the de-trackmargin obtained when information was recorded on the groove and theland. A solid line s shows measured results of the de-track marginobtained when information was recorded on the groove, and a broken linet shows measured results of the de-track margin obtained wheninformation was recorded on the land. A dash-and-dot line M shows thede-track margin level. From these measured results, it is to beunderstood that the sufficient de-track margins could be obtained in anyof the above cases.

While the present invention uses the second optical recording medium 20which is recorded and reproduced by the FAD system and D-RAD system ofMSR in the above-mentioned examples, the present invention is notlimited to those examples, and the present invention can obtain a stablerecording and reproducing characteristic even when the present inventionis applied to other system in which a magnetic domain is transferred andthereby enlarged and other system in which a magnetic wall is displaced.

In particular, the present invention uses magnetic wall displacement anddomain enlargement type MSR systems, these systems have characteristicsfrom a recording and reproducing standpoint in which a reproducingmagnetic field required when these systems function is not required.Thus, if these systems are applied to the present invention, then whencompatibility with the MD is obtained, the apparatus can be simplifiedmore in arrangement, accordingly, the apparatus can be made compact insize and light in weigh and further a cost of the apparatus can bedecreased.

As set forth above, according to the present invention, since it becomespossible to use the MD that is now widely used, recorded information canbe used significantly and a large-storage capacity optical recordingmedium with a high recording density necessary for recording andreproducing moving picture information whose demand will increase morecan be used by an apparatus having the same optical system. At the sametime, its recording and reproducing characteristic can be held stably,and hence it is possible to provide an optical recording and reproducingmethod and an optical recording medium which are extremely advantageousfor practical use.

1. An optical recording and reproducing method for recording and reproducing data from at least two types of optical recording media comprising: generating recording and/or reproducing light with a wavelength selected in a range of 780 nm±10 nm and transmitting the light via an objective lens with a numerical aperture NA selected in a range of from 0.45±0.01; reproducing data from first and second optical recording mediums with different recording capacities, said first optical recording medium having a track pitch in a range of from 1.5 μm to 1.7 μm and a groove depth in a range of from 70 nm to 90 nm, and said second optical recording medium having a track pitch in a range of from 1.2 μm to 1.3 μm and a groove depth in a range of from 150 nm to 180 nm.
 2. The optical recording and reproducing method according to claim 1, wherein said first and second optical recording mediums are magneto-optical recording mediums.
 3. The optical recording and reproducing method according to claim 2, wherein said first optical recording medium has at least a first dielectric layer, a magneto-optical recording layer, a second dielectric layer and a thermal diffusion layer deposited over a substrate, in that order, and said second optical recording medium has at least a first dielectric layer, a first magneto-optical recording layer, a second magneto-optical recording layer, a third magneto-optical recording layer and a second dielectric layer deposited over a substrate, in that order, and said second magneto-optical recording layer having a Curie temperature selected to be small as compared with Curie temperatures of said first and third magneto-optical recording layers.
 4. The optical recording and reproducing method according to claim 3, wherein said magneto-optical recording layer of said first optical recording medium is comprised of either TbFeCo or TbFeCoCr, and said first magneto-optical recording layer of said second optical recording medium is comprised of any one of GdFeCo, GdFe, GdFeCoCr, GdFeCoAl or GdFeCoSi, said magneto-optical recording layer of said second optical recording medium is comprised of any one of TbFe, TbFeCo, TbFeAl, TbFeCr, TbFeSi, TbFeCoAl, TbFeCoCr or TbFeCoSi, and said third magneto-optical recording layer of said second optical recording medium is comprised of either TbFeCo or TbFeCoCr.
 5. The optical recording and reproducing method according to claim 1, wherein said second optical recording medium is a magneto-optical recording medium containing information which is reproduced by a magnetically induced super resolution (MSR) system, said second optical recording medium having a recording capacity greater than 1 GB.
 6. The optical recording and reproducing method according to claim 5, wherein said second optical recording medium is a magneto-optical recording medium in which information is recorded by a groove recording system.
 7. The optical recording and reproducing method according to claim 5, wherein said second optical recording medium is a magneto-optical recording medium in which information is recorded by a land-groove recording system.
 8. An optical recording and reproducing method for recording and reproducing data comprising: generating recording and/or reproducing light with a wavelength selected in a range of 780 nm±10 nm and transmitting the light via an objective lens with a numerical aperture NA selected in a range of from 0.45±0.01; and reading data from an optical recording medium with the light, characterized in that the optical recording medium has a track pitch in a range of from 1.2 μm to 1.3 μm and a groove depth in a range of from 150 nm to 180 nm.
 9. The optical recording and reproducing method according to claim 8, wherein said optical recording medium is a magneto-optical recording medium.
 10. The optical recording and reproducing method according to claim 9, wherein said magneto-optical recording medium has at least a first dielectric layer, a first magneto-optical recording layer, a second magneto-optical recording layer, a third magneto-optical recording layer and a second dielectric layer, in that order, and said second magneto-optical recording layer having a Curie temperature selected to be small as compared with those of said first and third magneto-optical recording layers.
 11. The optical recording and reproducing method according to claim 10, wherein said first magneto-optical recording layer of said optical recording medium is comprised of any one of GdFeCo, GdFe, GdFeCoCr, GdFeCoAl or GdFeCoSi, said second magneto-optical recording layer of said optical recording medium is comprised of anyone of TbFe, TbFeCo, TbFeAl, TbFeCr, TbFeSi, TbFeCoAl, TbFeCoCr or TbFeCoSi, and said third magneto-optical recording medium of said optical recording medium is comprised of either TbFeCo or TbFeCoCr.
 12. The optical recording and reproducing method according to claim 8, wherein said optical recording medium is a magneto-optical recording medium containing information reproduced by a magnetically induced super resolution system, and said magneto-optical recording medium having a recording capacity greater than 1 GB.
 13. The optical recording and reproducing method according to claim 12, wherein said optical recording medium is a magneto-optical recording medium in which information is recorded by a groove recording system.
 14. The optical recording and reproducing method according to claim 12, wherein said optical recording medium is a magneto-optical recording medium in which information is recorded by a land-groove recording system. 